The present invention relates to a solventless one-pack type epoxy resin composition and a cured product thereof. More particularly, it relates to a solventless one-pack type epoxy resin composition comprising a low-viscosity epoxy resin and an acid anhydride hardener that is an imide oligomer having an imide unit and an acid anhydride group at the terminal, and a cured product obtained from the resin composition.
As the level of integration of semiconductor chips increases, flip chip packages in which a chip and a substrate are connected via bumps have been taking the place of chip-on-board packages such as pin grid array packages in which a chip and a substrate are connected by wire bonding. Spot sealing of the flip chip packages is carried out by using, as an underfill sealant, a flowable solventless one-pack type epoxy resin composition.
With the increasing integration scale of circuits to be mounted, the substrates have also been changing from rigid materials such as glass-epoxy laminates to flexible films. However, conventionally employed underfill materials have insufficient adhesion to a polyimide film used in tape carrier packages due to their high elastic modulus and therefore insufficient reliability. JP-A-9-153570 proposes an underfill material containing butadiene rubber particles and thereby having a reduced elastic. modulus, but the butadiene rubber particles are difficult to disperse uniformly only to provide an underfill material with insufficient reliability in long term use.
An object of the present invention is to provide a solventless one-pack type epoxy resin composition which provides a cured resin having a small elastic modulus and good adhesion to both a silicon wafer and a polyimide film and which exhibits satisfactory molding properties such as a low viscosity and capability of penetrating in a relatively short time.
Another object of the present invention is to provide a cured resin having a low elastic modulus and a high adhesive strength.
The present invention relates to a one-pack type epoxy resin composition which comprises a low-viscosity epoxy resin and an acid anhydride hardener that is an imide oligomer comprising an imide unit and having an acid anhydride group at the terminal thereof, the imide unit being represented by formula I: 
wherein A represents an asymmetric aromatic tetracarboxylic dianhydride residue or alicyclic tetracarboxylic dianhydride residue; and B represents a diaminopolysiloxane residue, and has a viscosity of 250 P or less at 25xc2x0 C.
The present invention also relates to a cured resin obtained by thermally curing the above described one-pack type curable epoxy resin composition.
In this specification, xe2x80x9chalf-esterificationxe2x80x9d means esterification of tetracarboxylic dianhydride to dicarboxylic acid diester. xe2x80x9cPenetrabilityxe2x80x9d, xe2x80x9cpenetrationxe2x80x9d and xe2x80x9cpenetratingxe2x80x9d mean that the epoxy resin composition flows inwardly to fill a gap between a flip chip and a substrate due to the capillary phenomenon.
The preferred embodiments of the present invention will be, described below.
1) In the one-pack type epoxy resin composition, the acid anhydride hardener is an imide olygomer having an acid anhydride group at the terminal thereof and having an A moiety to B moiety molar ratio of 1.2 to 5.
2) In the one-pack type epoxy resin composition, the acid anhydride hardener is an imide oligomer having an acid anhydride group at the terminal thereof which is obtainable by once half-esterifying an asymmetric aromatic tetracarboxylic dianhydride or alicyclic tetracarboxylic dianhydride (A moiety) with an esterifying agent, particularly aliphatic alcohols having 4 or less carbon atoms, and then adding a diaminopolysiloxane (B moiety) to the reaction mixture at an A moiety to B moiety molar ratio of 1.2 to 5 to cause the reaction mixture to dehydrate until substantially no solvent remains in the reaction system.
3) In the one-pack type epoxy resin composition, the acid anhydride hardener is an imide oligomer having an acid anhydride group at the terminal thereof which is obtainable by using an alicyclic tetracarboxylic dianhydride represented by formula II: 
4) In the one-pack type epoxy resin composition, the acid anhydride hardener is present in an amount of 5% by weight or more, particularly 5-75% by weight based on the composition and of 1 equivalent or less, particularly 0.9-1.0 equivalent per equivalent of the total epoxy group content.
5) The one-pack type epoxy resin composition further comprises an alicyclic acid anhydride hardener, a phenolic resin hardener or both in such an amount that the total content of the functional groups of all hardeners is 1 equivalent or less, particularly 0.9-1.0 equivalent per equivalent of total epoxy group content of the low-viscosity epoxy resin.
6) The one-pack type, epoxy resin composition thermally cures to provide a cured resin having a tensile modulus of 200 kg/mm2 or less, particularly 1-200 kg/mm2, more particularly 1-150 kg/mm2 at 25xc2x0 C.
7) The one-pack type epoxy resin composition further comprises a silane coupling agent.
8) The one-pack type epoxy resin composition is used as an underfill material for an electronic component.